Articular cartilage is the remarkably durable tissue that covers the articulating bone surfaces in our joints and permits pain-free movement by greatly reducing friction between bones and distributing stress. Unfortunately, when cartilage is damaged due to injury or disease, it has a limited capacity to heal and can lead to premature arthritis. Arthritis is a major health issue that is predicted to increase as our population ages. As such, there is considerable interest in the development of techniques to repair or reconstruct damaged articular cartilage. The implications of a successful method for cartilage repair would be great in terms of the number of patients affected and their quality of life. Importantly, in this era of escalating health care costs, successful cartilage repair would decrease the long-term costs of health care related to joint replacement and multiple revisions thereof. Our long-term objective is to develop a tissue engineering approach for cartilage repair using periosteum. Periosteal grafts have the potential to contribute to each of the three requirements for tissue engineering (scaffold, cells, growth factors), and have been used successfully in biological resurfacing for the repair of damaged articular cartilage. The principle obstacle to overcome for the use of periosteal tissue grafts for tissue engineering is the declining chondrogenic potential of periosteum with increasing age of the patient. We hypothesize that subperiosteal injection of specific growth factors can be used as a pretreatlnent to "activate" periosteum for articular cartilage tissue engineering. In essence, the engineered tissue will be prepared in vivo for transplantation. In this proposal, we plan to examine the potential for subperiosteal injection of known chondrogenic growth factors to enhance (1) the number of chondrogenic precursor cells in periosteum in vivo (Aim 1), (2) the in vitro chondrogenic potential of periosteum (Aim 2) and (3) the potential of periosteum to repair articular cartilage defects (Aim 3). Beyond articular cartilage repair, these studies have the potential to impact the use of periosteum for other applications such as tissue engineering of bone. In addition, by eliminating the need for cell culture expansion facilities and expertise, the cost of this approach should be considerably less thereby making cartilage repair more globally accessible.